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billplate

why r Top and Bottom layers are full of gaps?

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I could be wrong, but to my inexpert eye, It looks less like under execution and more like the printer is over spacing between stroke of the print head, so i get stripes rather than a solid layer on top and to a lesser extent also on the bottom. The sides of my

prints look fine.

ive tightened up the runners so there's no movement and changing the materal has no affect on the problem.

can anyone suggest what the problem is and better still how to fix it? :)

extrution_issue_preview_featured.jpg

 

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You have two problems: underextrusion and backlash/play. They are completely unrelated to each other. You should fix both.

1) Underextrusion. Either your spring is not set ideally or something else. I assume this is a UMO. What temp, speed, and layer height are you printing at? Here's a graph that describes the relationship between these 3 variables - print at half the speed of the blue line or slower:

http://umforum.ultimaker.com/index.php?/topic/4127-um2-extrusion-rates-revisited/

Don't you dare post anything without answering my question in point #1.

2) backlash/play. This can be caused by loose belts or high friction. In either case the head doesn't move all the way to where the stepper commands it. On UMO the short belts (on the motors) are more likely a problem than the long belts. Loosen the 4 screws, push down on stepper and tighten. If the belts are *too* tight then friction can be too high. Also on UMO it's extremely common for the wooden end caps to be too tight. Try loosening 1 end cap on each of all 4 rotating axes in the top gantry. Do that while pushing the print head around. You should be able to easily move the print head with your smallest finger on each hand pushing on the outer blocks.

It's quite possible (likely even) that only one of your axes has excess play or excess friction.

 

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…..Layer hight 0.1mm

These setting r pretty standard for me, I don’t mess around much with the settings for Cura or the machines itself.

On your suggestions about belt tension I did try putting a tensioner on the back Y axis belt, as it felt a bit slacker than the others. Don’t know if it would have helped as I had to remove it due to snagging which then resulted in it getting drawn into the wheels/rollers :( also it caused even worse slack in the front Y belt. My sense is you guys r right and the belt is the culprit.

Gr5 I did your slow print test, 0.2mm at 30mm/s this didn’t seem to have any effect on the striping though.

Any more thoughts or advice r more than welcome

thanks

 

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underextrusion

If you had followed my link you would see that at .1mm, 210C, .4mm nozzle 120mm/sec is the absolute fastest the UM2 can print. 100mm/sec is pushing close to that limit and I'm not surprised you have some underextrusion. I recommend not going over 60mm/sec or alternatively raise the temp to 240C (this is not a random temp - it's right off the graph as the minimum temp to print at if you want to print at half the max possible speed). It is quite possible that your machine has degraded a bit. This is common as the feeder can get ground up and also the isolator can get compressed/deformed or you are getting towards the end of a reel and the filament is more curved and getting more stuck in the bowden and isolator. There's lots more suggestions about testing for underextrusion and fixing issues elsewhere. But your problem might be too minor to fix at this early stage as you are printing right near the absolute limit.

play/backlash

From your description it sounds like one of the sides of a long belt is tight and the other side of the same belt is loose. This is most likely the cause of your backlash and takes about 30 seconds to fix. Loosen the small allen screw that holds the pulley tight on either end and the belt should quickly even out the tension on both sides. If not, then something is wrong with the existing tensioner which is *inside* the black block. Make sure to retighten the pulley - tight as all hell. The allen wrench should twist quite a bit.

 

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As dimensioner hints - another possibility is that your nozzle isn't set to .4 in cura or your shell width isn't a multiple of .4. For example if you set the shell to 1mm then the UM2 will try to overextrude *all* infill (not just the shell) and it will print the shell in two .5mm passes and then all the infill will also be at .5mm which is tough to squeeze out of a .4mm nozzle resulting in some underextrusion also.

ALWAYS set the shell to a multiple of the nozzle. Especially when printing at the absolute top limit of what the UM2 can do.

 

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hay guys

the nozzle is still set to 0.4mm.

gr5 although i follow the logic im surprised to here what u saying about the working in mutably of the nozzle diameter, simply because the Cura default shell setting is 0.6mm. mostly i left it on that because ive had no reason to chang it till now. But ill up it too 0.8 if u think that's a better for the machine and or print quality?

As I said, I did follow the link and your directions u gave. The first set of setting I gave were the once id been using before.

Below is a pic of a print from your 0.2mm layer at 30mm/s speed.

Anyway, returning to the stripes. While loosening the pulleys I discover the problem, Im almost certain it’s the short belt on right stepper. Its very slack compared to the other side and u can see it flinch / slip when it changes direction.

Do I simply have to replace it?

(insistently i canceled the print on its second layer once it was clear it was still doing stripes, the layer below looks better simply because it's the bottom layer)

loos_belt_preview_featured.jpg

 

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No, you can tighten the short belts by loosening the screws on the stepper mottor and pressing down on it (down as in the same direction as the gravity exerts power on the stepper) and then at the same time tighten the screws again. You'll have do to it a few times until you get a matching tension on both short belts.

 

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gr5 although i follow the logic im surprised to here what u saying about the working in mutably of the nozzle diameter, simply because the Cura default shell setting is 0.6mm.

 

You are possibly mixing up the shell thickness with the bottom/top thickness. The default cura settings for shell thickness is 0.8mm. The bottom/top thickness is 0.6mm (which is 6x the default layer height).

(on Cura 14.12.1)

 

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